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  • Two-key encryption/decryption?

    - by Matt
    I'm looking to store some fairly sensitive data using PHP and MySQL and will be using some form of reversible encryption to do so since I need to get the data back out in plain text for it to be of any use. I'll be deriving the encryption key from the users' username/password combination but I'm stumped for what to do in the (inevitable) event of a password being forgotten. I realise that the purpose of encryption is that it can only be undone using the correct key but this must have been addressed before.. I'm trying to get my head around whether or not public key cryptography would apply to the problem but all I can think of is that the private key will still need to be correct to decrypt the data.. Any ideas?

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  • Is a many-to-many relationship with extra fields the right tool for my job?

    - by whichhand
    Previously had a go at asking a more specific version of this question, but had trouble articulating what my question was. On reflection that made me doubt if my chosen solution was correct for the problem, so this time I will explain the problem and ask if a) I am on the right track and b) if there is a way around my current brick wall. I am currently building a web interface to enable an existing database to be interrogated by (a small number of) users. Sticking with the analogy from the docs, I have models that look something like this: class Musician(models.Model): first_name = models.CharField(max_length=50) last_name = models.CharField(max_length=50) dob = models.DateField() class Album(models.Model): artist = models.ForeignKey(Musician) name = models.CharField(max_length=100) class Instrument(models.Model): artist = models.ForeignKey(Musician) name = models.CharField(max_length=100) Where I have one central table (Musician) and several tables of associated data that are related by either ForeignKey or OneToOneFields. Users interact with the database by creating filtering criteria to select a subset of Musicians based on data the data on the main or related tables. Likewise, the users can then select what piece of data is used to rank results that are presented to them. The results are then viewed initially as a 2 dimensional table with a single row per Musician with selected data fields (or aggregates) in each column. To give you some idea of scale, the database has ~5,000 Musicians with around 20 fields of related data. Up to here is fine and I have a working implementation. However, it is important that I have the ability for a given user to upload there own annotation data sets (more than one) and then filter and order on these in the same way they can with the existing data. The way I had tried to do this was to add the models: class UserDataSets(models.Model): user = models.ForeignKey(User) name = models.CharField(max_length=100) description = models.CharField(max_length=64) results = models.ManyToManyField(Musician, through='UserData') class UserData(models.Model): artist = models.ForeignKey(Musician) dataset = models.ForeignKey(UserDataSets) score = models.IntegerField() class Meta: unique_together = (("artist", "dataset"),) I have a simple upload mechanism enabling users to upload a data set file that consists of 1 to 1 relationship between a Musician and their "score". Within a given user dataset each artist will be unique, but different datasets are independent from each other and will often contain entries for the same musician. This worked fine for displaying the data, starting from a given artist I can do something like this: artist = Musician.objects.get(pk=1) dataset = UserDataSets.objects.get(pk=5) print artist.userdata_set.get(dataset=dataset.pk) However, this approach fell over when I came to implement the filtering and ordering of query set of musicians based on the data contained in a single user data set. For example, I could easily order the query set based on all of the data in the UserData table like this: artists = Musician.objects.all().order_by(userdata__score) But that does not help me order by the results of a given single user dataset. Likewise I need to be able to filter the query set based on the "scores" from different user data sets (eg find all musicians with a score 5 in dataset1 and < 2 in dataset2). Is there a way of doing this, or am I going about the whole thing wrong?

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  • In R, how do you get the best fitting equation to a set of data?

    - by Matherion
    I'm not sure wether R can do this (I assume it can, but maybe that's just because I tend to assume that R can do anything :-)). What I need is to find the best fitting equation to describe a dataset. For example, if you have these points: df = data.frame(x = c(1, 5, 10, 25, 50, 100), y = c(100, 75, 50, 40, 30, 25)) How do you get the best fitting equation? I know that you can get the best fitting curve with: plot(loess(df$y ~ df$x)) But as I understood you can't extract the equation, see Loess Fit and Resulting Equation. When I try to build it myself (note, I'm not a mathematician, so this is probably not the ideal approach :-)), I end up with smth like: y.predicted = 12.71 + ( 95 / (( (1 + df$x) ^ .5 ) / 1.3)) Which kind of seems to approximate it - but I can't help to think that smth more elegant probably exists :-) I have the feeling that fitting a linear or polynomial model also wouldn't work, because the formula seems different from what those models generally use (i.e. this one seems to need divisions, powers, etc). For example, the approach in Fitting polynomial model to data in R gives pretty bad approximations. I remember from a long time ago that there exist languages (Matlab may be one of them?) that do this kind of stuff. Can R do this as well, or am I just at the wrong place? (Background info: basically, what we need to do is find an equation for determining numbers in the second column based on the numbers in the first column; but we decide the numbers ourselves. We have an idea of how we want the curve to look like, but we can adjust these numbers to an equation if we get a better fit. It's about the pricing for a product (a cheaper alternative to current expensive software for qualitative data analysis); the more 'project credits' you buy, the cheaper it should become. Rather than forcing people to buy a given number (i.e. 5 or 10 or 25), it would be nicer to have a formula so people can buy exactly what they need - but of course this requires a formula. We have an idea for some prices we think are ok, but now we need to translate this into an equation.

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  • Code won't exit foreach block

    - by Matt
    I've got the following C# code segment that takes a list, finds objects that are ready to update, then shoves them into a temp list, deletes from the main list, and then goes on its merry way. My issue is that the foreach block, which cycles through my main list, won't exit. TempLog.Clear(); //Ensure TempLog is empty foreach (CLogger ready in PlayerLog) { if (ready.UpdateReady == true) // Record is ready to be updated in database { TempLog.Add(ready); // Add record to templog PlayerLog.Remove(ready); // Remove from playerlog } } <---- Never reaches this point if (TempLog.Count > 0) // Just check that templog isn't empty { new Thread(Update).Start(); // Run update code } I've put heaps of debugging in, and I can watch PlayerLog start at 1, TempLog at 0, then it enters the foreach loop, picks up that the record UpdateReady flag is on, TempLog goes to 1, PlayerLog goes to 0, then it just stops.. No errors, just stops.. Thanks for the help :)

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  • My winform application doesn't work on others' pc without vs 2010 installed

    - by wings
    Just like I said, my winform application works properly on computers with VS installed, but on other computers, it will crash due to a FileNotFound Exception. I used using Application = Microsoft.Office.Interop.Excel.Application; in my source code to generate a Excel file, and the problem occurs as soon as the Excel-related function is called. But I don't know what it refers to exactly. Do I have to get some .dll included along with the .exe file? And what DLL is that? Below are part of my codes: private void FileExport(object objTable) { StartWaiting(); string[,] table = null; try { table = (string[,])objTable; } catch (Exception ex) { ShowStatus(ex.Message, StatusType.Warning); } if (table == null) { return; } Application excelApp = new Application { DisplayAlerts = false }; Workbooks workbooks = excelApp.Workbooks; Workbook workbook = workbooks.Add(XlWBATemplate.xlWBATWorksheet); Worksheet worksheet = (Worksheet)workbook.Worksheets[1]; worksheet.Name = "TABLE"; for (int i = 0; i < table.GetLength(0); i++) { for (int j = 0; j < table.GetLength(1); j++) { worksheet.Cells[i + 1, j + 1] = table[i, j]; } } Range range = excelApp.Range["A1", "H1"]; range.Merge(); range.Font.Bold = true; range.Font.Size = 15; range.RowHeight = 50; range.EntireRow.AutoFit(); range = excelApp.Range["A2", "H8"]; range.Font.Size = 11; range = excelApp.Range["A1", "H8"]; range.NumberFormatLocal = "@"; range.RowHeight = 300; range.ColumnWidth = 50; range.HorizontalAlignment = XlHAlign.xlHAlignCenter; range.VerticalAlignment = XlVAlign.xlVAlignCenter; range.EntireRow.AutoFit(); range.EntireColumn.AutoFit(); worksheet.UsedRange.Borders.LineStyle = 1; Invoke(new MainThreadInvokerDelegate(SaveAs), new object[] { worksheet, workbook, excelApp } ); EndWaiting(); }

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  • Minutia on Objective-C Categories and Extensions.

    - by Matt Wilding
    I learned something new while trying to figure out why my readwrite property declared in a private Category wasn't generating a setter. It was because my Category was named: // .m @interface MyClass (private) @property (readwrite, copy) NSArray* myProperty; @end Changing it to: // .m @interface MyClass () @property (readwrite, copy) NSArray* myProperty; @end and my setter is synthesized. I now know that Class Extension is not just another name for an anonymous Category. Leaving a Category unnamed causes it to morph into a different beast: one that now gives compile-time method implementation enforcement and allows you to add ivars. I now understand the general philosophies underlying each of these: Categories are generally used to add methods to any class at runtime, and Class Extensions are generally used to enforce private API implementation and add ivars. I accept this. But there are trifles that confuse me. First, at a hight level: Why differentiate like this? These concepts seem like similar ideas that can't decide if they are the same, or different concepts. If they are the same, I would expect the exact same things to be possible using a Category with no name as is with a named Category (which they are not). If they are different, (which they are) I would expect a greater syntactical disparity between the two. It seems odd to say, "Oh, by the way, to implement a Class Extension, just write a Category, but leave out the name. It magically changes." Second, on the topic of compile time enforcement: If you can't add properties in a named Category, why does doing so convince the compiler that you did just that? To clarify, I'll illustrate with my example. I can declare a readonly property in the header file: // .h @interface MyClass : NSObject @property (readonly, copy) NSString* myString; @end Now, I want to head over to the implementation file and give myself private readwrite access to the property. If I do it correctly: // .m @interface MyClass () @property (readonly, copy) NSString* myString; @end I get a warning when I don't synthesize, and when I do, I can set the property and everything is peachy. But, frustratingly, if I happen to be slightly misguided about the difference between Category and Class Extension and I try: // .m @interface MyClass (private) @property (readonly, copy) NSString* myString; @end The compiler is completely pacified into thinking that the property is readwrite. I get no warning, and not even the nice compile error "Object cannot be set - either readonly property or no setter found" upon setting myString that I would had I not declared the readwrite property in the Category. I just get the "Does not respond to selector" exception at runtime. If adding ivars and properties is not supported by (named) Categories, is it too much to ask that the compiler play by the same rules? Am I missing some grand design philosophy?

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  • Best way to implement game loop without freezing UI thread

    - by Matt H
    I'm trying to make a simple 2D game in Java. So far I have a JFrame, with a menubar, and a class which extends JPanel and overrides it's paint method. Now, I need to get a game loop going, where I will update the position of images and so on. However, I'm stuck at how best to achieve this. Should I use multi-threading, because surely, if you put an infinite loop on the main thread, the UI (and thus my menu bar) will freeze up? Here's my code so far: import java.awt.Color; import java.awt.Graphics; import javax.swing.JPanel; @SuppressWarnings("serial") public class GameCanvas extends JPanel { public void paint(Graphics g) { while (true) { g.setColor(Color.DARK_GRAY); try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } } } } import javax.swing.JFrame; import javax.swing.JMenu; import javax.swing.JMenuBar; import javax.swing.JMenuItem; @SuppressWarnings("serial") public class Main extends JFrame { GameCanvas canvas = new GameCanvas(); final int FRAME_HEIGHT = 400; final int FRAME_WIDTH = 400; public static void main(String args[]) { new Main(); } public Main() { super("Game"); JMenuBar menuBar = new JMenuBar(); JMenu fileMenu = new JMenu("File"); JMenuItem startMenuItem = new JMenuItem("Pause"); menuBar.add(fileMenu); fileMenu.add(startMenuItem); super.add(canvas); super.setVisible(true); super.setSize(FRAME_WIDTH, FRAME_WIDTH); super.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); super.setJMenuBar(menuBar); } } Any pointers/tips? Also, where should I put my loop? In my main class, or my GameCanvas class? Any help is appreciated, thanks.

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  • Which database engines support IP addresses as a native type?

    - by Matt McClellan
    I'm trying to find databases with support for IP addresses as a native type (as opposed to storing as a string, or an unsigned integer, which at least one commenter has already pointed out won't work for IPv6). The primary reason I'm looking for this is ease of development. For example, sorting on a "native" IP address column would be correct (as opposed to when it's stored as a string). I would assume support for such a type would also include useful operations such as determining if an IP address is inside a specified network for use in WHERE clauses. The only one I'm aware of so far is PostgreSQL with its inet class. Does anyone have any others?

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  • How to fetch, display Amazon Marketplace listings by item?

    - by Matt G.
    Hi all, My question pretty much says it all: I'm looking for a way to display Amazon Marketplace listings based on an item lookup. Example: If I do a call to ItemLookup with an ASIN of 0590353403 (Harry Potter and the Sorcerer's Stone), I'm looking for a result set of perhaps the top ten new or used Marketplace listings, preferably with seller information attached. I apologize if this is clearly documented somewhere, but I have been looking all through the Amazon API docs and on Google to no avail. StackOverflow doesn't seem to have any Related Questions that match what I'm asking, either. Thanks in advance!

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  • Multithreaded Delegates/Events

    - by Matt
    I am trying to disable parts of the UI in a .NET app based on polling done on a background thread. The background thread checks to see if the global database connection the app uses is still open and operable. What I need to do, and would prefer to do it without polling on the UI thread, is to add an event handler that can be raised by the background thread if the connection status changes. That way, any form can have a handler that will disable those parts of the UI that require the connection to function. Attempting to use a straight event declaration in the class that holds the thread sub, and raising the event in the background thread causing cross-thread execution errors regarding accessing UI controls from other threads. Obviously, there is a correct way to do this, but we have limited experience with events (single threaded apps mainly), and almost none with delegates. I've read through documentation and examples for delegates, and it seems to be closer to what we need, but I'm not sure how to make it work in this instance. The app is written mainly in VB.NET, but an example or help in C# is fine too.

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  • Basic problems (type inference or something else?) in Objective-C/Cocoa.

    - by Matt
    Hi, Apologies for how basic these questions are to some. Just started learning Cocoa, working through Hillegass' book, and am trying to write my first program (a GUI Cocoa app that counts the number of characters in a string). I tried this: NSString *string = [textField stringValue]; NSUInteger *stringLength = [string length]; NSString *countString = (@"There are %u characters",stringLength); [label setStringValue:countString]; But I'm getting errors like: Incompatible pointer conversion initializing 'NSUInteger' (aka 'unsigned long'), expected 'NSUInteger *'[-pedantic] for the first line, and this for the second line: Incompatible pointer types initializing 'NSUInteger *', expected 'NSString *' [-pedantic] I did try this first, but it didn't work either: [label setStringValue:[NSString stringWithFormat:@"There are %u characters",[[textField stringValue] length]]] On a similar note, I've only written in easy scripting languages before now, and I'm not sure when I should be allocing/initing objects and when I shouldn't. For example, when is it okay to do this: NSString *myString = @"foo"; or int *length = 5; instead of this: NSString *myString = [[NSString alloc] initWithString:"foo"]; And which ones should I be putting into the header files? I did check Apple's documentation, and CocoaDev, and the book I'm working for but without luck. Maybe I'm looking in the wrong places.. Thanks to anyone who takes the time to reply this: it's appreciated, and thanks for being patient with a beginner. We all start somewhere. EDIT Okay, I tried the following again: [label setStringValue:[NSString stringWithFormat:@"There are %u characters",[[textField stringValue] length]]] And it actually worked this time. Not sure why it didn't the first time, though I think I might have typed %d instead of %u by mistake. However I still don't understand why the code I posted at the top of my original post doesn't work, and I have no idea what the errors mean, and I'd very much like to know because it seems like I'm missing something important there.

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  • Cannot add or update a child row: a foreign key constraint fails

    - by Tom
    table 1 +----------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +----------+-------------+------+-----+---------+----------------+ | UserID | int(11) | NO | PRI | NULL | auto_increment | | Password | varchar(20) | NO | | | | | Username | varchar(25) | NO | | | | | Email | varchar(60) | NO | | | | +----------+-------------+------+-----+---------+----------------+ table2 +------------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +------------------+--------------+------+-----+---------+----------------+ | UserID | int(11) | NO | MUL | | | | PostID | int(11) | NO | PRI | NULL | auto_increment | | Title | varchar(50) | NO | | | | | Summary | varchar(500) | NO | | | | +------------------+--------------+------+-----+---------+----------------+ com.mysql.jdbc.exceptions.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (myapp/table2, CONSTRAINT table2_ibfk_1 FOREIGN KEY (UserID) REFERENCES table1 (UserID)) What have I done wrong? I read this: http://www.w3schools.com/Sql/sql_foreignkey.asp and i don't see whats wrong. :S

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  • How is location accuracy measured in Android?

    - by John Palmer
    Does anyone know the proper interpretation of the accuracy measurements returned by getAccuracy()? For instance, are they calculated as: Circular Error Probability (meaning, if i understand correctly, radius of a 50% confidence circle)? Radius of 95% confidence circle? something else? Many thanks for any advice you can give me.

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  • Java: Calculate distance between a large number of locations and performance

    - by Ally
    I'm creating an application that will tell a user how far away a large number of points are from their current position. Each point has a longitude and latitude. I've read over this article http://www.movable-type.co.uk/scripts/latlong.html and seen this post http://stackoverflow.com/questions/837872/calculate-distance-in-meters-when-you-know-longitude-and-latitude-in-java There are a number of calculations (50-200) that need carried about. If speed is more important than the accuracy of these calculations, which one is best?

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  • Get substring between "\" where multiple "\"

    - by AceAlfred
    Found this solution to get substring after slash () character DECLARE @st1 varchar(10) SET @st1 = 'MYTEST\aftercompare' SELECT @st1 ,SUBSTRING(@st1, CHARINDEX('\', @st1) + 1, LEN(@st1)) http://social.msdn.microsoft.com/Forums/sqlserver/en-US/5c3a5e2c-54fc-43dd-b12c-1a1f6784d7d8/tsql-get-substring-after-slash-character But is there a way to get substring after second slash or even more? DECLARE @st1 varchar(50) --Added more slashes SET @st1 = 'MYTEST\aftercompare\slash2\slash3\slash4' SELECT @st1 --This part would need some work --,SUBSTRING(@st1, CHARINDEX('\', @st1) + 1, LEN(@st1)) And getting only the substring between the slashes. Values: [1] "aftercompare" - [2] "slash2" - [3] "slash3" - [4] "slash4"

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  • IPhone: different system timers??

    - by matt
    I have been using mach_absolute_time() for all my timing functions so far. calculating how long between frames ect. I now want to get the exact time touch input events happen using event.timestamp in the touch callbacks. the problem is these two seem to use completely different timers. sure, you can get them both in seconds, but their origins are different and seemingly random... is there any way to sync the two different timers? or is there anyway to get access to the same timer that the touch input uses to generate that timestamp property? otherwise its next to useless.

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  • Java class Class<T> and static method Class.forName() drive me crazy.

    - by matt
    Hi, this code doesn't compile. i'm wandering what i am doing wrong: private static Importable getRightInstance(String s) throws Exception { Class<Importable> c = Class.forName(s); Importable i = c.newInstance(); return i; } where Importable is an interface and the string s is the name of an implementing class. The compiler says: ./Importer.java:33: incompatible types found : java.lang.Class<capture#964 of ?> required: java.lang.Class<Importable> Class<Importable> c = Class.forName(format(s)); thanks for any help!

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